The answer, it turns out, is 144 — and the formula used to get to that answer is what's now known as the Fibonacci sequence. Read more: 9 equations that changed the world "Liber Abaci" first ...

This diagram shows how the number of pairs of rabbits over time forms the Fibonacci sequence. (Wikimedia Commons CC BY-SA 3.0)If you start with one pair, you soon get two pairs, three, five, eight ...